Catalysts for thermal cure silicone release coatings

ABSTRACT

An environmentally acceptable catalyst, coating system, and methods for thermal cure silicone release coatings that utilize bismuth (“Bi”) catalyst to retain properties of tin (“Sn”)-catalyzed systems but do not have the toxicity and environmental hazards associated therewith. The coating systems and methods also provide a laminate that shows reduced orange peel distortion over time compared with tin (“Sn”)-catalyzed systems and methods.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is continuation of U.S. patent application Ser. No.13/689,996, filed on Nov. 30, 2012, now pending, which is a Continuationof International Application Number PCT/US12/66858, filed Nov. 28, 2012,now expired and also claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/566,122, filed Dec. 2, 2011, now expired.International Application Number PCT/US12/66858, filed Nov. 28, 2012,now expired, also claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/566,122, filed Dec. 2, 2011, now expired. Theentire disclosure of both documents is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure is related to the field of silicone release coatingtechnology. Specifically using catalysts containing bismuth (bismuth(“Bi”) catalysts) for thermal curing of silicone release coatings.

2. Description of Related Art

Release coatings are generally used to prevent things from stickingtogether. This simple statement and function encompasses a broad base oftechnology and a large global industry involving both silicone andnon-silicone materials. A very common release coating in the industryutilizes thermal curing based generally on the following reaction:

In the above reaction, a high molecular weight silanol prepolymer (suchas α,ω-dihydroxysilanol of polydimethylsiloxane (PDMS) structure whichhas a molecular weight of about 5 kg/mol) reacts with a lower molecularweight silane (such as one with a molecular weight of about 2 kg/mol).The high functionality of the silane provides for the crosslinking ofthe silanol and the resultant curing of the coating through theformation of an infinite 3D polymeric network. The reaction proceedsslowly at room temperature, but dramatically accelerates in the presenceof a catalyst and under elevated temperatures. The reaction isdehydrogenative condensation which is accompanied by evolution ofdihydrogen.

The first thermal-cure silicone release coating systems werecommercialized in the 1950s and used tin based materials as thecatalyst. Since that time, several technological revolutions haveoccurred including solvent-based platinum (“Pt”)-catalyzed thermalcuring systems in the 1970s, followed by solventless platinum (“Pt”)-and rhodium (“Rh”)-catalyzed systems, radiation curing systems andlow-temperature curing systems. It should be recognized that terminologyin this area can be a bit confusing. When one refers to a platinum(“Pt”)-catalyzed curing system, or platinum (“Pt”) catalyst, thecatalyst generally does not comprise only platinum metal, instead, itgenerally means that a compound including that metal is used. Thisterminology will be used throughout this disclosure, and thus any phraseindicating that the curing system is metal (“Me”)-catalyzed or there isa metal (“Me”) catalyst should be taken to mean that the catalyst is acompound including the metal “Me”, not necessarily the metal itself.

Despite these changes in thermal cure solvent-based release coatingsystems, tin (“Sn”) catalyst cure systems are still heavily utilized inrelease coatings. In these reactions, organo-tin compounds, such asdibutyltin diacetate, in the presence of moisture, catalyze thereaction. Tin (“Sn”)-catalyzed condensation cure systems are stillgenerally well used in the art because of their inherent properties.First, the rates of tin (“Sn”)-catalyzed condensation cure systems areslow at room temperatures, becoming faster at higher temperatures.Further, many commonly used manufacturing systems in the art haveanchorage and pot life requirements, for which the slow cure times oftin (“Sn”)-catalyzed systems are ideal. In certain cases low-temperaturecure is often desirable because it reduces energy costs and facilitatesthe coating of temperature-sensitive film substrates.

Second, tin (“Sn”)-catalyzed silicone release coating systems are morecost effective. Tin (“Sn”)-catalyzed systems are relatively inexpensive,especially when compared to platinum (“Pt”)- or rhodium (“Rh”)-catalyzedsystems, which are extremely expensive. Third, tin (“Sn”)-catalyzedsilicone release coating systems are extremely robust. For example, tin(“Sn”)-catalyzed systems are resistant to substrate inhibition, thusallowing for a wider choice of possible substrates. Finally, there isgenerally little adhesive interaction with tin (“Sn”)-catalyzed systemswhich can be valuable in applications involving silicone laminates.Furthermore, release coatings are usually solvent-borne systems whichallow coatings as thin as about 100 nm on a substrate. In sum, tin(“Sn”)-catalyzed silicone release coating systems provide for awell-established, reliable, low-cost coating system that can be coatedonto a wide selection of substrates. For this reason, tin(“Sn”)-catalyzed silicone release coating systems are preferred in manyareas of the art.

However, despite these advantages, due to environmental concerns andregulatory restrictions there has been pressure to move away from tin(“Sn”)-catalyzed systems. While some in the art have adjusted to thesenew environmental concerns and regulatory pressure by moving towardsplatinum (“Pt”)- or rhodium (“Rh”)-catalyzed systems or solventless,emulsion-based and UV-cure technologies, none of these systems have thesame inherent advantages of tin (“Sn”)-catalyzed silicone releasecoating systems. Thus, these alternative systems generally do not meetcustomer demands for a catalyzed release coating that functionssimilarly to a tin (“Sn”)-catalyzed release coating. Further, due toincreased costs of alternative catalysts, among other factors, thesesystems are not as cost-effective for producers and manufacturers in theart as the tin (“Sn”)-catalyzed systems.

Because of these cost considerations and behavioral differences insolventless, emulsion-based, platinum (“Pt”)- or rhodium(“Rh”)-catalyzed systems and UV-cure technologies, there is a very highdemand in the industry for a catalyst for silicone release coatingsystems that is cost effective and has the same behavioralcharacteristics as known for tin (“Sn”)-catalyzed systems. Stateddifferently, a replacement catalyst is needed that can be used insteadof catalysts comprising tin compounds in silicone release coatingsystems that will retain all of the advantageous properties of tin(“Sn”)-catalyzed systems without any of the toxicity hazards associatedwith the tin (“Sn”)-catalyzed systems.

SUMMARY

An environmentally acceptable catalyst, coating system, and methods forthermal cure silicone release coatings that utilize bismuth (“Bi”)catalyst to retain properties of tin (“Sn”)-catalyzed systems but do nothave the toxicity and environmental hazards associated therewith. Thecoating systems and methods also provide a laminate that shows reducedorange peel distortion over time compared with tin (“Sn”)-catalyzedsystems and methods.

There are described herein, among other things, a method of forming asilicone release coating according to the following reaction:

utilizing a bismuth (“Bi”) catalyst in the thermal curing.

There is also described herein, a method of forming a silicone releasecoating comprising: mixing a solvent, a silanol, a silane, and bismuth(“Bi”) catalyst to form a mixture; and thermally curing said mixture toform a silicone release coating. The method of claim 2 furthercomprising adding a reactive siloxane polymer to the mixture prior tothermal curing.

In embodiments of the method, the method may further comprise one ormore of: adding a silanol pre-polymer to the mixture prior to thermalcuring; adding a pre-polymer crosslinker, such as, but not limited to, asilane with functionality, f_(Si-H), of 2 or higher to the mixture priorto thermal curing; adding amino silicone to the mixture prior to thermalcuring; adding a control release additive, such as, but not limited to,a silicone resin, for example, an M resin or MQ resin, to the mixtureprior to thermal curing; or adding an inhibitor to the mixture prior tothermal curing.

In an embodiment of the method, the bismuth (“Bi”) catalyst is selectedfrom the group consisting of: a bismuth-zinc neodecanoate, a bismuth2-ethylhexanoate, a metal carboxylate of bismuth and zinc, and a metalcarboxylate of bismuth and zirconium.

In an embodiment of the method, the bismuth (“Bi”) catalyst comprisesbismuth in combination with at least one metal selected from the groupconsisting of: zinc, zirconium, titanium, palladium, and aluminum orsaid bismuth (“Bi”) catalyst comprises a bismuth salt or bismuthchelate.

There is also described herein a method of storing a rolled film, themethod comprising: mixing a solvent, a silanol, a silane, and a catalystincluding bismuth to form a mixture; coating a liner with the mixture;thermally curing the mixture to form a silicone release coating on theliner; applying the silicone release coating to a film; rolling at least1000 feet of said film and liner in a bulk roll; and retaining the filmand liner in said bulk roll for more than two days, in some embodimentsat least 5 days; wherein, after the retaining, the film has less orangepeel distortion than if said silicone release coating had been formedwith catalyst including tin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 demonstrate the aging of the liquid formulations for siliconerelease liners in the presence of bismuth (“Bi”) catalysts. In thiscase, a bismuth/zinc neodecanoate mixture, as further discussed below,was used.

FIGS. 4-6 demonstrate the aging of the liquid formulations for siliconerelease liners in the presence of nickel (“Ni”) catalysts. In this case,nickel (II) octanoate, as further discussed below, was used.

FIGS. 7-8 demonstrate the aging of the liquid formulations for siliconerelease liners in the presence of iron (“Fe”) catalysts. In this case,iron acetate, as further discussed below, was used.

FIGS. 9-10 demonstrate the aging of the liquid formulations for siliconerelease liners in the presence of rhodium (“Rh”) catalysts. In thiscase, rhodium octanoate dimer, as further discussed below, was used.

FIG. 11 shows a comparison of average detected orange peel (averagedacross both the machine direction (MD) and transverse direction (TD) ofsamples of bismuth (“Bi”) catalysts and a tin (“Sn”) catalysts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Described herein is an environmentally acceptable catalyst and/orcoating system for thermal cure silicone release coatings that retainsthe inherent advantageous properties associated with tin(“Sn”)-catalyzed silicone release coatings but does not have thetoxicity and environmental hazards associated with the tin-basedsystems. As discussed above, the terminology used throughout thisdisclosure provides that any phrase indicating that the curing system ismetal (“Me”)-catalyzed or there is a metal (“Me”) catalyst should betaken to mean that the catalyst is a compound including the metal “Me”,not necessarily the metal itself. Thus, for example, a “tin(“Sn”)-catalyzed silicone release coating” is any silicone releasecoating formed utilizing a compound including elemental tin as acatalyst and a “bismuth (“Bi”) catalyst” is any compound includingelemental bismuth which can be used as a catalyst.

Unexpectedly, it has been found that bismuth compounds catalyze thecrosslinking of condensation-type silicone release coatings with similarrates and resultant properties as tin compounds. Experimentationrevealed that the tin (“Sn”) catalyst in silicone release coatings canbe replaced with a bismuth (“Bi”) catalyst at the same or lower atomicconcentrations (on a molar basis of the metal content) to acceleratecrosslinking and produce the same favorable inherent properties withoutthe hazards and toxicity associated with tin (“Sn”) catalysts. Althoughthese bismuth (“Bi”) catalysts can be used in any silicone releasecoatings, the coatings will generally include, in addition to thecatalyst: (1) a reactive siloxane polymer (referred to herein as“polysiloxane”), or, alternatively, a silanol pre-polymer; (2) apre-polymer crosslinker (referred to herein as “cross-linking agent”);(3) an optional control release additive; and (4) other optionaladditives (including, for example, an inhibitor).

In particular, in one embodiment, it was found that a bismuth(“Bi”)-catalyzed system, such as one with a bismuth/zinc catalyst isfour times more efficient than a conventional tin (“Sn”) catalyst on amole-to-mole basis of the metal content and produced the same inherentperformance properties as systems that were tin (“Sn”)-catalyzed. Assuch, a release liner with the same properties can be obtained if abouta quarter of the amount on a molar basis of the bismuth (“Bi”) catalystis used in place of a traditional tin (“Sn”) catalyst in the samecoating formulation.

The bismuth (“Bi”) catalysts are optimally used in an amount of about 2to 14 wt % based on the weight of the polysiloxane in the coatingformulation. The resultant release liner coating formulations used forthe examples of the application contained the following typicalcomponents in the following ranges (all amounts are in weight %):Catalyst: about 1.6-2.8; Polysiloxane or Silanol Prepolymer: about56-92; Cross-Linking Agent: about 0.89-2.00; Accelerator/Inhibitor:about 2.15-3.95; and an optional Control Release Additive: about 0-40.The particular components are discussed more fully below.

Solvent may be also added as necessary to the above formulations, asdetermined by one skilled in the art, to provide a coating that willmeet the specific requirements for thickness and other properties. Theamount of solvent depends on various factors, including the coatingmethod and particular coating equipment and process variables used. Inthe formulations tested, the solvent used was a mixture of heptane andtoluene in a weight ratio of about 1.7 to 2.05. The solvent mixture wasused in an amount of about 17 to 28 times the combined weight of theformulation components. Other solvents, and the ratios and amountsthereof, could be utilized as would be recognized by one of ordinaryskill in the art.

This disclosure proceeds with a more thorough discussion of theabove-noted components of the silicone release liner composition,followed by some of the findings associated with experimentation of thecompositions disclosed herein.

Polysiloxanes are well known in the art of silicone release liners. Thepolysiloxane, when crosslinked (in the presence of the catalyst),provides the base composition of the release liner coatings. Anypolysiloxane known to be used in silicone release liners can be utilizedin the composition disclosed herein, but the polysiloxane will generallycontain groups which can undergo condensation reactions, with the groupsbeing condensable with one another or with other reactive (i.e.,hydrolysable) leaving groups like alkoxy, aryloxy, alkylcarboxy, amidoand amino groups attached to silicon and the like. The preferred groupsare hydroxyl functional groups at the ends and/or along the polymerchain of the polysiloxane. More specifically, the composition disclosedherein is preferably comprised of hydroxyl-terminating (i.e., SiOH)polydimethylsiloxanes. Examples of such polysiloxanes are disclosed, forexample, in U.S. Pat. Nos. 3,527,659, 3,579,469, and 7,846,550, DE 15 46410, DE 21 35 673, and DE 27 48 406, the entire disclosures of which areincorporated herein by reference.

Alternatively, a silanol pre-polymer can be utilized in place of thepolysiloxane. The silanol pre-polymer will have functionality,f_(Si-OH), of greater than or equal to 2. The main backbone of thesilanol can be, for example, diphenylsiloxane or methylphenylsiloxane.Besides phenyl and methyl side groups the silanols may have n-, iso- ortertiary alkyl groups (C₂-C₃₇), cyclic alkyl groups, arylsubstitutedalkyl groups, carboxy groups, substituents with N, O, S or F-atoms andthe like. The silanol may be a copolymer or a mixture of silanols.Instead of silanols one can use silicone prepolymers with such terminalhydrolysable groups as aryloxy, alkoxy, alkylcarboxy, amido, and aminogroups.

The polysiloxane bearing Si—OH groups or the silicone pre-polymer(silonol) is generally cross-linked with a silane in the formation ofthe release coating. The salines can have the same or similar backbonesand substituents as those described above for silaols. It is desirableto have silanes of lower molecular weight than the molectular weight (tobe consistent with the next paragraph) of silanols and to have someexcess Si—H groups as compared to Si—OH groups in the reaction mixture.

As noted above, the crosslinking agent, as the name implies, crosslinksthe polysiloxane or the silanol pre-polymer to a cured surface layerwith release properties. The crosslinking agents are generally silanesand will generally have the same or similar backbones and substituentsas those described above for silanols and polysiloxanes. It isimportant, however, that the functionality, f_(Si-H), of silane is 2 orhigher. Further, it is preferred to have silanes of lower molecularweight than the molecular weight of the silanols or polysiloxanes. Thisensures that there are excess Si—H groups as compared to Si—OH groups inthe reaction mixture.

Amino silicone can also be added in the composition. The amino siliconemay have different structures than outlined above for silanol andsilane. Amino silicone has at least one primary, secondary, tertiary,etc. amino group bound to the backbone.

Control release additives such as silicone resins of the general formulaR_(n)Sio_((4-n)/2), where n is 0 to 4 and where R is generally ahydrocarbon, such as methyl (—CH₃) or phenyl (—C₆H₅) may be used can beused in some embodiments. A polymer having repeat units of [—SiR₂O—]would be referred to as a polysiloxane, and if R group was a methyl, itwould specifically be referred to as a poly(dimethylsiloxane). Theseresins are generally described using standard silicone M, D, T, Qnomenclature to describe silicone resins or siloxanes, where M, D, T andQ are described as follows: “M” designates the monofunctional unit,R₃SiO_(1/2) where the R groups may be the same or different; “D”designates the difunctional unit, R₂SiO_(2/2), where the R groups may bethe same or different; “T” designates the trifunctional unit, RSiO_(3/2)and “Q” designates the quadrifunctional unit, SiO_(4/2). The dimerR₃SiOSiR₃ (or (CH₃)₃SiO(CH₃)₃ if the R groups are methyl) would bereferred to as “MM” or “M₂” resin. The oligomer R₃Si[OSiR₂]_(x)OSiR₃ (or(CH₃)₃Si[OSi(CH₃)₂]_(x)OSi(CH₃)₃ if the R groups are methyl) would bereferred to as “MD_(x)M” resin, where “x” represents the number of “D”units in the chain. The cyclic trimer [SiR₂O]₃ (or [Si(CH₃)₂O]₃ if the Rgroups are methyl) would be referred to as “D₃” resin. The variousfragments (M, D, T and Q) are bonded together in various combinationsvia alternating [—Si—O—Si—O-Si—] linkages to make linear or non-linearsiloxane resins. In an embodiment, an MQ resin (which comprises both Munits and Q units or molecular fragments in various ratios of M to Q,depending on the desired properties) is used as the control releaseadditive. Such additives can also be utilized to increase the releaseforce, if necessary and/or desired, of the release liner. In thisregard, control release additives are not necessary, but, for someapplications, a wide range of release levels may be desired. Foradditional detail on silicone resins useable as control releaseadditives see J. E. Mark, H. R. Allcock, R. West, Inorganic Polymers,Oxford University Press, New York, 2005, chapter 4.3, the entiredisclosure of which is herein incorporated by reference.

Finally, it has now been discovered that the base reaction betweensilanol and silane can be catalyzed with a compound containing bismuth(a bismuth (“Bi”) catalyst). Generally, any bismuth compound, ormixtures containing bismuth compounds, known to those of ordinary skillin the art can be used as a bismuth (“Bi”) catalytic agent in siliconerelease coatings as disclosed herein. More specifically, contemplatedbismuth compounds are generally carboxylic salts of bismuth (III) andinclude bismuth in combination with metals like zinc, zirconium,titanium, palladium, and/or aluminum and salts or chelates of bismuth,preferably conveniently soluble in non-polar organic media. Some ofthese compounds have an excess of the corresponding acid to diminish thehydrolysis of bismuth (III). Examples of suitable bismuth compoundsinclude, but are not limited to: a bismuth-zinc neodecanoate mixturewith about 8 wt % bismuth (e.g., BiCAT® 8); bismuth 2-ethylhexanoatemixture with about 28 wt % bismuth (e.g., BiCAT® 8210); bismuthneodecanoate mixture with a low concentration of acid and about 28 wt %bismuth (e.g., BiCAT® 8124); and metal carboxylates of bismuth, zinc,and zirconium, with less than about 18 wt % bismuth (e.g., BiCAT® 3184).All the BiCAT® brand products are available from Shepard ChemicalCompany. Alternatively, the following bismuth compounds: bismuthcarboxylate with about 18 to 20 wt % bismuth (e.g., K-KAT® XC-B221 andK-KAT® XK-601); and bismuth carboxylate with no extra acid and about 31wt % bismuth (e.g., K-KAT® XK-628) can be used. All of these K-KAT®brand compounds are available from King Chemical Company. It is believedthat bismuth acetate with no extra acid and about 54 wt % bismuth wouldalso work, however, it is generally insoluble in the components of thereaction and would likely require an additional agent to provide forappropriate mixing.

Surprisingly, experimentation based on the composition disclosed hereinrevealed that the peel force necessary to peel off test tape fromrelease coatings (also known as a release force and discussed more fullybelow) in bismuth (“Bi”)-catalyzed silicone release coatings wasstatistically the same peel force necessary to peel off test tape fromtin (“Sn”)-catalyzed silicone release coatings. This was true even whenthe same base coating formulations were used with different controlrelease additive (MQ resin) concentrations. While peel release values(“PRV”) did sometimes change between catalysts (particularly withaltering concentrations), the numbers were generally sufficientlysimilar, and other properties were generally similar, to allow forbismuth (“Bi”)-catalyzed coating systems to be used as a substitute fortin (“Sn”)-catalyzed coating systems.

For example, in a series of experiments, peel release values of avariety of release liners prepared with either a tin (“Sn”)-catalyzedsystem or a bismuth (“Bi”)-catalyzed system, such as a bismuth/zinccatalyst, were compared to each other. The release liners prepared witha bismuth (“Bi”) catalyst had an elemental bismuth atomic concentrationof about 25% of the elemental tin present in a tin (“Sn”) catalyst. Theonly difference between the coating formulations was the amount and typeof elemental metal (i.e., elemental tin or elemental bismuth). The samePRV values were obtained for each release liner tested irrespective ofthe elemental metal and the specific metal compound utilized so long asappropriate amounts of the specific catalyst were used. Stateddifferently, with appropriate selection of the amount of catalyst, therewas no substantial statistical difference in the PRV of any of therelease liners tested, regardless of which specific elemental metal orcatalyst compound was utilized (i.e., either tin or bismuth).

In one experiment with a liner manufactured with a tin (“Sn”)-catalyzedsystem, a peel force of 27.4 g-force/in was attained. When the tin(“Sn”) catalyst was replaced by the bismuth (“Bi”) catalyst(specifically bismuth/zinc (e.g., BiCAT® 8) or bismuth (BiCAT® 8210)) inthe same release liner coating formulation in a concentration usingbismuth (“Bi”) catalyst in an amount of about 75 wt. % of the amount ofthe tin (“Sn”) catalyst, peel forces of about 25 and about 23 g-force/inrespectively were obtained. In sum, the same (statistically) PRV valueswere obtained for each release liner formulation that was testedirrespective of whether catalysts comprising elemental bismuth or tinwere used. Substituting bismuth (“Bi”) catalysts for the traditional tin(“Sn”) catalysts provided a release liner that was more environmentallyfriendly without sacrificing the advantageous physical and mechanicalproperties obtained by tin (“Sn”)-catalyzed silicone release coatings.

In addition, the degree of cure measured by extraction (as discussedmore fully below) from a coated cured film kept in n-heptane wasstatistically the same for both tin (“Sn”)- and bismuth (“Bi”)-catalyzedsilicone release coatings in each of the prepared and tested releaseliners. For example, one silicone coated release liner which was testedwith both tin (“Sn”)-catalyzed and bismuth (“Bi”)-catalyzed systems hadabout 16% extractables with a tin (“Sn”) catalyst and about 10%extractables with a bismuth (“Bi”) catalyst. Thus, experimentationrevealed that bismuth (“Bi”) catalysts are unexpectedly more efficientcatalysts than tin (“Sn”) catalysts and can be utilized at the same orlower concentrations in silicone release coatings without sacrificing oraltering the performance properties traditionally associated with tin(“Sn”)-catalyzed systems.

This discovery of the analogous properties of bismuth (“Bi”) catalystswas even more surprising given that bismuth (“Bi”) catalysts succeededwhere other catalysts, with compounds having similar structures to tin(“Sn”) catalysts, had failed. Comparative experiments were performedusing other catalysts with similar structures to tin carboxylates. Whensubstituted for tin (“Sn”) catalysts, these other catalysts did notaccelerate crosslinking at room temperature. Other catalysts testedincluded zinc (“Zn”) catalysts (zinc stearate and zinc neodecanoate),iron (“Fe”) catalyst (iron acetate), nickel (“Ni”) catalyst (nickeloctanoate hydrate), and rhodium (“Rh”) catalyst (rhodium octanoatedimer). All of these other catalysts were tested in the same basecoating formulations, and they all demonstrated poor coating performance(as tested by smoothing a finger or thumb over the coating and visuallyobserving whether the coating smeared or smudged, as discussed morefully below). All of the catalysts were tested at the same level, andall except the zinc neodecanoate were partially soluble. The iron (“Fe”)catalysts, nickel (“Ni”) catalysts, and rhodium (“Rh”) catalysts, whenused, made colored solutions, providing evidence that at least somecatalyst was in solution. While there was some catalytic activity fromthe zinc (“Zn”)-catalyzed systems, the zinc (“Zn”)-catalyzed coatingswere not as robust as the bismuth (“Bi”)-catalyzed (e.g. bismuth/zinc)systems. The nickel (“Ni”) catalysts and iron (“Fe”) catalysts, whentested in this application, did not demonstrate any catalytic properties(i.e. no curing).

This poor efficiency of the iron (“Fe”)-catalyzed, nickel(“Ni”)-catalyzed, and rhodium (“Rh”)-catalyzed systems with regard toacceleration of crosslinking is demonstrated in FIGS. 1-10. FIGS. 1-3are three IR spectra which demonstrate the aging of a liquid siliconeformulation used for release liners consisting of commercially availablecomponents and having a bismuth/zinc compound used instead of anelemental tin compound in the catalyst. The spectrum in FIG. 1 was takenpromptly after preparation of the bismuth (“Bi”)-catalyzed formulation,and it demonstrates a relatively weak but measurable absorption band at2160 cm⁻¹ due to Si—H vibrations of the silane curing agent. Asdemonstrated in FIG. 2, taken after 4 days of storage at roomtemperature, the band decreases in intensity. Further, as seen in FIG.3, after 6 days of storage at room temperature the band disappearscompletely. This was originally taken to signify that crosslinking hasoccurred and the silane curing agent has been used up. However, it hasbeen determined that as the coating formulations include an excess ofsilane curing agent, it should not be entirely consumed in the reaction.However, a catalyst containing bismuth apparently reacts with raw silanecuring agent to eliminate the peak and indicate curing. The absence ofthe peak is therefore indicative (but does not necessarily prove) thatthe material has cured.

FIGS. 4-6 show spectra taken at the same time frame with the samerelease coating formulation as in FIGS. 1-3, but with a nickel (“Ni”)catalyst. FIGS. 7-10 show spectra taken promptly after preparation andafter 6 days of storage at room temperature with the same releasecoating formulation as in FIGS. 1-3, but with an iron (“Fe”) catalyst(FIGS. 7-8) and a rhodium (“Rh”) catalyst (FIGS. 9-10) rather than abismuth (“Bi”) catalyst. These Figures demonstrate a very lowconsumption of Si—H, leading to the conclusion that catalysts havingnickel, iron, and rhodium compounds are poor catalysts for siliconecrosslinking. Specifically, the films prepared with nickel, iron, andrhodium compounds as the catalysts (at equivalent elemental metal atomicconcentrations of tin (“Sn”) catalyst) had smudgy surfaces, leavingone's fingerprint on a surface when rubbed or smudged. Specifically, afinger pushed against the surface removed material in the form of anunset viscous liquid as opposed to scuffing a delicate solid. Thisindicated that the films had not cured showing the relevance of thespectral peak's presence. This leads to the conclusion that the siliconerelease coatings that utilized these catalysts were not sufficientlycured.

In contrast, films prepared with tin (“Sn”) and bismuth (“Bi”) catalystsunder the same process conditions had glossy surfaces, were curedsufficiently, and exhibited the same mechanical and release properties.Given that other catalysts with a structure similar to tin carboxylatesdid not cure the silicone release agents, it was surprising andunexpected that bismuth (“Bi”)-catalyzed silicone release agents curedat the same or lower concentrations and under the same conditions as tin(“Sn”)-catalyzed coatings and had the same mechanical and releaseproperties.

Another unexpected advantage of using bismuth (“Bi”)-catalyzed siliconerelease coatings compared with the traditional tin (“Sn”)-catalyzedsilicone release coatings is a reduction in orange peel distortion inthe adhesive bonded to the release liner.

Silicone release liners consisting of a silicone coated PET film areoften used to protect optically clear pressure sensitive adhesives. Suchadhesives might be used in solar control films or electronic displays,for example, where distortion-free transparency of the adhesive isparamount. One form of distortion very common in this type of adhesiveis orange peel distortion, so called because of its appearancereminiscent to that of the surface of an orange when viewing theadhesive layer at an angle. Excessive orange peel distortion renders thecoated adhesive unusable because of poor visual (or optical) quality inthe end-use product such as solar control film.

Orange peel distortion appears to come into play when rolls of laminateutilizing silicone release liners are formed which are woundparticularly tight and may be caused by pressure on the film, slippageof component parts relative to each other, or other effects orcombinations of effects. However, orange peel distortion generally isworse closer to the core of a large roll of laminate (as it would havemore tension on the laminate closer to the core) one examines, and thelonger that the laminate is maintained on the roll instead of in smallerrolls.

Because the deleterious effects of orange peel distortion are ultimatelyseen by eye, adhesive-coated transparent film products are generallyinspected by eye after manufacture using a visual grading scale. Onesuch scale ranges from 0 to 5 where an adhesive coating of grade 0 hasno discernible orange peel distortion while one of grade 5 might havevery bad orange peel distortion. A pass-fail grade is set within thescale, for example grades 0 to 3 pass and 4 to 5 fail quality inspectionand require reworking or disposal. With training and experience andaided by reference samples, individuals can assess a particular filmsample accurately and reproducibly.

Proper comparisons of orange peel distortion in two film samples canonly be made if adhesive coating and lamination of the release liner iscarried out on a roll-to-roll coating machine rather than preparingsheet samples in the laboratory. Two release liners were made withsilicone coatings according to the formulations of Sample 1 in Table 1(below), using dibutyltin diacetate catalyst, and Sample 4 in Table 3(below), using the BICAT® 8 catalyst. These release liners were thenlaminated to identical rolls of pressure-sensitive adhesive coated PETfilm. The adhesive was a typical solvent-based polyacrylate pressuresensitive adhesive manufactured by, for example, Henkel Corporation.Samples were taken from 5000 ft rolls of laminate at different times andpositions through the rolls and assessed for orange peel distortionvisually and with tests across both the machine direction (MD—thedirection that the material is wound) and the transverse direction(TD—the direction perpendicular to the direction the material is wound)which sometimes show slightly different effects.

FIG. 11 shows that laminates made from both tin (“Sn”)- and bismuth(“Bi”)-catalyzed silicone release liners exhibit orange peel distortionmeasured visually that generally increases with time and depth into theroll of film that the samples were taken from (i.e., increases as thesamples get closer to the core). However, as can be seen, while thebismuth (“Bi”)-catalyzed liner showed a greater in distortion after 1day (line (101)) compared to the tin (“Sn”)-catalyzed liner (line(103)), the bismuth (“Bi”)-catalyzed liner showed a lower level oforange peel distortion after 5 days (line (111)) than the tin(“Sn”)-catalyzed liner (line (113)). Furthermore, the bismuth(“Bi”)-catalyzed liner is associated with a laminate in which orangepeel distortion is more stable both over time and through the roll oflaminate as the lines (101) to (111) do not shift upward as much as thelines (103) and (113) and are flatter throughout the roll. This shows alaminate that appears to be significantly more stable over time.

It is differences in the level of orange peel distortion at these longertimes that is most commercially significant. Rolls of laminate made in1000 foot, 2000 foot, 5000 foot, 10000 foot, or longer ‘bulk’ rolls, forexample, are generally cut down into smaller rolls, such as 100 footrolls, for sale. The quicker distortion develops, which often increasesas the bulk roll gets bigger, the quicker these smaller sale-size rollsmust be created (that is, the quicker the bulk rolls must be cut downinto smaller rolls and not stored as bulk rolls). In most prior cases,if sale-size rolls were not created within about one or two days ofmaking a ‘bulk’ roll, the laminate could become so distorted as torender a good portion, if not all the bulk roll, unusable due to theorange peel distortion. It has been shown that once sale-size rolls(e.g. 100 foot) are created, the laminate is stabilized and the amountof distortion does not significantly increase over time. This inabilityto keep bulk rolls longer than about 2 days due to the distortionseverely reducing manufacturing flexibility and ultimately removes theoption of supplying ‘bulk’ rolls to the marketplace or storing certainlaminates in bulk form until needed. Instead, additional warehousing isrequired to store large numbers of smaller sale-size rolls andtransportation, packaging and handling costs are increased as materialmust be shipped after being cut into smaller rolls, which take up morespace than one large roll.

For these reasons, the difference in FIG. 11 between the behavior of thetin (“Sn”)-catalyzed and the bismuth (“Bi”)-catalyzed release linersafter five days is most significant. The ability to maintain a bulk rollfor any additional period of time provides for flexibility in storageand transportation. A bulk roll which previously would be unusable orunsalable after two days can now be stored for five days (thus allowingthe roll to be stored longer), and more importantly, allowing for theroll to be shipped a greater distance prior to it needing to be brokendown into smaller, sale-sized rolls.

The bismuth (“Bi”) catalysts and the bismuth (“Bi”)-catalyzed coatingsdisclosed herein while particularly discussed in conjunction withsilicone release liners can also be useful for other silicone end-useapplications, such as other silicone polymers, including roomtemperature vulcanizable (RTV) silicone elastomers and sealants thatcurrently use tin catalysts such as stannous octoate or dibutyltindilaurate.

The presently described composition and associated coatings will now bedescribed with reference to the following non-limiting examples.However, before turning to the examples, it is useful to have anunderstanding of the tests by which some of the properties andcharacteristics of the coatings are measured.

As noted above, peel release value (PRV) of the cured coating is theforce required to peel an adhesive from a release liner and istraditionally measured in g-force/in. A test tape (3M 610 tape orToray's Tesa® 7475) of approximately ten (10) inches is applied with a4.5 pound calibrated hand rubber roller to a five-day old cured releaseliner coating. After one (1) hour, the tape is peeled from the releaseliner coating at a rate of 90 inches per minute and a peel height(height of the mechanical arm gripping the tape) of 1.75 inches. Themeasurements of PRV are then performed with a peel tester such as theIMASS SP-2000 or 2100 of IMASS, Inc. The release liners disclosed hereinresulted in a PRV of 3 to 300 g-force/in.

The coating performance of the release liners can be tested anddescribed in a variety of ways and based on different valuations. In afirst test (named the Smudge Test herein) a finger is rubbed over therelease liner coating, and then, the coating is observed to see whetherthere is a smear or smudge on the coating. Second, the “ExtractionPercentage” of the cured coatings can be determined. A square piece ofrelease liner with a cured coating of dimensions 5″×5″ is submerged into200 mL of hexane for 30 min. The thickness of coating is measured (byX-ray fluorescence spectrometry of elemental Si with a properparameterization of the fluorometer) both before and after the liner issubmerged in the hexane. It is preferred that the coating decreases inthickness by no more than 15% as a result of extraction. Third, the“readhesion test” can measure the coating performance of the releaseliner with respect to transfer of silicone to the adhesive surface. Atest tape is applied to stainless steel (6″ length) and the PRV₀ ismeasured. A fresh piece of tape is then applied to the cured coatingsand removed. The same piece of tape (that was applied to the curedcoating) is applied to a clean stainless steel surface the same way andthe PRV₁ is measured. In a preferred embodiment, the PRV₁ is at least85% of PRV₀, meaning that little silicone coating has been transferredto the adhesive tape surface (or that most of the coating remained onthe liner). In other words, the coating is robust in that the degree ofcontamination of the tape by the coating is small. Finally, the “Si—H IRDisappearance” can be measured. The IR spectra of the release linercomposition is measured which demonstrates the aging of a liquidsilicone formulation. More specifically, the Si—H vibrations of silanecuring agent can result in a spectral absorption band at 2160 cm⁻¹ whichis indicative that the silicone coating has not cured (as discussedabove). However, the disappearance of this absorption band is a strongindication that curing has occurred. The cured coatings disclosed hereindemonstrate the complete disappearance of a relatively weak butmeasurable absorption band at 2160 cm⁻¹ in ATR IR spectrum of the curedcoating.

Examples 1-3

Coating solution with tin (“Sn”) catalysts were first prepared ascomparative examples. Varying amounts of solvent (toluene and heptane);silanol (SS4191A); silane (SS4191B); amino silane (SS4259C); controlrelease additive (“CRA”) (MQ resin, SS4215); all of which are availablefrom Momentive™ Performance Materials and the catalyst (dibutyltindiacetate) were all mixed together to form the compositions shown belowin Table 1. The values given are masses based on a total solution ofabout 200 grams. The molecular weight of these components varies frombatch to batch but is approximately 500, 4.5, 2, and 4 kg/mol,respectively, for the silanol, CRA, silane, and amino silicone.

TABLE 1 Components Sample 1 Sample 2 Sample 3 Toluene 58.5 48.5 52.1Heptane 101.1 98.4 89.2 Silanol 36.7 37.4 32.9 Silane 0.6 0.5 0.5 AminoSilane 1.5 1.4 1.3 CRA 0.0 12.5 22.7 Catalyst 1.5 1.4 1.3

The compositions were applied to a PET film by a hand draw down. Theliquid coatings and the PET substrate were then thermally cured in aconvection oven at 300° F. for approximately 60 seconds. The resultingproduct was then tested according to the above described methods.

TABLE 2 Test Sample 1 Sample 2 Sample 3 Smudgy No Some Some Thickness,nm 110 100 105 Extraction 14% 11% 12% PRV, g-force/in  9  34  51 (610tape) PRV Readhesion 88% 93% 91% Si—H IR Complete Complete CompleteDisappearance

As can be seen, the addition of the CRA leads to an increase of PRV. TheCRA also improves the adhesion of the silicone release liner to the PET.However, the tin (“Sn”) catalyst in the presence of the CRA did resultin some smudginess in the liner.

Examples 4-6

Varying amounts of solvent (toluene and heptane); silanol (SS4191A);silane (SS4191B); amino silane (SS4259C); control release additive (MQresin—SS4215); and catalyst (bismuth-zinc neodecanoate mixture withabout 8 wt % bismuth) were all mixed together to form the compositionsshown below in Table 3. The values given are masses based on a totalsolution of about 200 grams. The molecular weight of these componentsvaries from batch to batch but is approximately 500, 4.5, 2, and 4kg/mol, respectively, for the silanol, CRA, silane, and amino silane.

TABLE 3 Components Sample 4 Sample 5 Sample 6 Toluene 58.5 48.5 52.1Heptane 101.1 98.4 89.2 Silanol 36.7 37.4 32.9 Silane 0.6 0.5 0.5 AminoSilane 1.5 1.4 1.3 CRA 0.0 12.5 22.7 Catalyst 1.1 1.1 1.0

The compositions were applied to a PET film by a hand draw down. Theliquid coatings and the PET substrate were then thermally cured in aconvection oven at 300° F. for approximately 60 seconds. The resultingproduct was then tested according to the above described methods.

TABLE 4 Test Sample 4 Sample 5 Sample 6 Smudgy No No No Thickness, nm 95115 100 Extraction 12% 11% 10% PRV, g-force/in 10  35  58 (610 tape) PRVReadhesion 87% 90% 93% Si—H IR Complete Complete Complete Disappearance

As can be seen from a comparison of Tables 2 and 4, the formulation ofbismuth (“Bi”) catalyst (i.e., bismuth-zinc neodecanoate mixture withabout 8 wt % bismuth) leads to similar properties as tin (“Sn”)catalyzed formulations. In fact, the bismuth (“Bi”) catalyst is fourtimes more efficient (on an elemental metal basis) than a conventionaltin (“Sn”) catalyst on a mole-to-mole basis. Additionally, bismuth(“Bi”)-catalyzed formulations produced the same inherent performanceproperties of release liners as systems that were tin (“Sn”)-catalyzed.As such, a release liner with the same properties can be obtained ifabout a quarter of the amount on a molar basis of the bismuth (“Bi”)catalyst (such as BiCAT® 8 bismuth/zinc) is used in place of atraditional tin (“Sn”) catalyst in the same coating formulation.

Examples 7-9

Varying amounts of solvent (toluene and heptane); silanol (SS4191A);silane (SS4191B); amino silane (SS4259C); control release additive (MQresin—SS4215); and catalyst (bismuth neodecanoate mixture with lowconcentration of acid and about 28 wt % bismuth) were all mixed togetherto form the compositions shown below in Table 5. The values given aremasses based on a total solution of about 200 grams. The molecularweight of these components varies from batch to batch but isapproximately 500, 4.5, 2, and 4 kg/mol, respectively, for the silanol,CRA, silan, and amino silane.

TABLE 5 Components Sample 7 Sample 8 Sample 9 Toluene 58.5 48.5 52.1Heptane 101.1 98.4 89.2 Silanol 36.7 37.4 32.9 Silane 0.6 0.5 0.5 AminoSilane 1.5 1.4 1.3 CRA 0.0 12.5 22.7 Catalyst 1.1 1.1 1.0

The compositions were applied to a PET film by a hand draw down. Theliquid coatings and the PET substrate were then thermally cured in aconvection oven at 300° F. for approximately 60 seconds. The resultingproduct was then tested according to the above described methods.

TABLE 6 Test Sample 7 Sample 8 Sample 9 Smudgy Some No No Thickness, nm110 105 120 Extraction 12% 13% 14% PRV, g-force/in  9  40  62 (610 tape)PRV Readhesion 86% 92% 94% Si—H IR Complete Complete CompleteDisappearance

As can be seen from a comparison of Tables 2 and 6, the formulation witha different bismuth (“Bi”) catalyst (i.e., bismuth neodecanoate mixturewith low concentration of acid and about 28 wt % bismuth) leads to quitesimilar properties as the tin (“Sn”)-catalyzed formulation as well asthose of the other bisnmuth (“Bi”) catalyst formulation.

Example 10

Solvent (toluene and heptane); silanol (SS4191A); silane (SS4191B);amino silane (SS4259C); and catalyst (bismuth carboxylate with no extraacid and about 28 wt % bismuth) were all mixed together to form thecomposition shown below in Table 7. The values given are masspercentages based on a total solution of about 200 grams. The molecularweight of these components varies from batch to batch but isapproximately 500, 4.5, 2, and 4 kg/mol, respectively, for the silanol,silane, and amino silicone.

TABLE 7 Components Sample 10 Toluene 58.5 Heptane 101.1 Silanol 36.7Silane 0.6 Amino Silane 1.5 CRA 0.0 Catalyst 1.1

The composition was applied to a PET film by a hand draw-down. Theliquid coating and the PET substrate were then thermally cured in aconvection oven at 300° F. for approximately 60 seconds. The resultingproduct was then tested according to the above described methods.

TABLE 8 Test Sample 10 Smudgy No Thickness, nm 95 Extraction 13% PRV,g-force/in  7 (610 tape) PRV Readhesion 90% Si—H IR CompleteDisappearance

As can be seen from a comparison of Tables 2 and 8, the formulation withyet another bismuth (“Bi”) catalyst (i.e., bismuth carboxylate with noextra acid and about 28 wt % bismuth) leads to similar properties as tin(“Sn”)-catalyzed formulations as well as formulations with the differentbismuth (“Bi”) catalysts.

While the inventions have been disclosed in conjunction with adescription of certain embodiments, including those that are currentlybelieved to be the preferred embodiments, the detailed description isintended to be illustrative and should not be understood to limit thescope of the present disclosure. As would be understood by one ofordinary skill in the art, embodiments other than those described indetail herein are encompassed by the present invention. Modificationsand variations of the described embodiments may be made withoutdeparting from the spirit and scope of any invention herein disclosed.

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present disclosurecan be used interchangeably with any ranges, values or characteristicsgiven for any of the other components of the disclosure, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout. Further, ranges provided for agenus or a category can also be applied to species within the genus ormembers of the category unless otherwise noted.

1. An environmentally acceptable reaction system for use in formingthermal cure silicone release coatings, said reaction system comprising:(a) a hydroxyl-terminated polysiloxane, a silanol prepolymer, or acombination thereof; (b) a silane cross-linking agent having a Si—Hfunctionality of at least 2; and (c) a catalyst component consistingessentially of a bismuth-containing carboxylate catalyst comprising inthe range of from 8 weight percent to 28 weight percent bismuth, basedon the total weight of said bismuth-containing carboxylate catalyst,wherein, when combined, said hydroxyl-terminated polysiloxane, silanolprepolymer, or combination thereof reacts with said silane cross-linkingagent in the presence of said catalyst component via a dehydrogenativecondensation reaction to thereby form a cross-linked polysiloxane. 2.The reaction system of claim 1, wherein said bismuth-containingcarboxylate catalyst further comprises at least one additional metalselected from the group consisting of zinc, zirconium, titanium,palladium, and aluminum.
 3. The reaction system of claim 1, wherein saidbismuth-containing carboxylate catalyst is selected from the groupconsisting of a bismuth-zinc neodecanoate catalyst, a bismuth2-ethylhexanoate catalyst, a metal carboxylate catalyst of bismuth andzinc, and a metal carboxylate catalyst of bismuth and zirconium.
 4. Thereaction system of claim 1, wherein said catalyst component consists ofsaid bismuth-containing carboxylate catalyst.
 5. The reaction system ofclaim 1, wherein said catalyst component is present in said reactionsystem in an amount of 2 to 14 weight percent, based on the total weightof said hydroxyl-terminated polysiloxane, silanol prepolymer, orcombination thereof.
 6. The reaction system of claim 1, furthercomprising at least one amino silicone.
 7. The reaction system of claim1, wherein said silane cross-linking agent has a lower molecular weightthan said hydroxyl-terminated polysiloxane, silanol prepolymer, orcombination thereof.
 8. The reaction system of claim 1, furthercomprising an inhibitor.
 9. A release liner comprising a liner andcoating layer formed on at least one surface of said liner, wherein saidcoating layer comprises said reaction system of claim
 1. 10. Anenvironmentally acceptable reaction system for use in forming thermalcure silicone release coatings, said reaction system comprising: (a) ahydroxyl-terminated polysiloxane, silanol prepolymer, or combinationthereof; (b) a silane cross-linking agent having a Si—H functionality ofat least 2; (c) a bismuth-containing carboxylate catalyst; and (d) atleast one amino silicone.
 11. The reaction system of claim 10, whereinsaid bismuth-containing carboxylate catalyst comprises in the range offrom 8 weight percent to 28 weight percent bismuth, based on the totalweight of said bismuth-containing carboxylate catalyst, and wherein saidbismuth-containing carboxylate catalyst is present in said reactionsystem in an amount of 2 to 14 weight percent, based on the total weightof said hydroxyl-terminated polysiloxane, silanol prepolymer, orcombination thereof.
 12. The reaction system of claim 10, wherein saidbismuth-containing carboxylate catalyst further comprises at least oneadditional metal selected from the group consisting of zinc, zirconium,titanium, palladium, and aluminum.
 13. The reaction system of claim 10,wherein said bismuth-containing carboxylate catalyst is selected fromthe group consisting of a bismuth-zinc neodecanoate catalyst, a bismuth2-ethylhexanoate catalyst, a metal carboxylate catalyst of bismuth andzinc, and a metal carboxylate catalyst of bismuth and zirconium.
 14. Thereaction system of claim 10, wherein said amino silicone is present insaid reaction system in an amount of 1.5 weight percent or less, basedon the total weight of said reaction system.
 15. The reaction system ofclaim 10, wherein said silane cross-linking agent has a lower molecularweight than said hydroxyl-terminated polysiloxane, silanol prepolymer,or mixture thereof, and wherein, when combined, said hydroxyl-terminatedpolysiloxane, silanol prepolymer, or combination thereof reacts withsaid silane cross-linking agent in the presence of saidbismuth-containing carboxylate catalyst via a dehydrogenativecondensation reaction to thereby form a cross-linked polysiloxane.
 16. Arelease liner comprising: (a) a coating layer formed from a reactionsystem, said reaction system comprising— (i) a silicone diol; (ii) asilane prepolymer cross-linking agent; and (iii) a bismuth-containingcarboxylate catalyst; and (b) a liner, wherein said coating layer isformed on at least one surface of said liner, wherein said release linerhas a peel release value (PRV) that is statistically the same as the PRVobtained from a comparative release liner identical to said releaseliner but including a comparative coating layer that uses a dibutyltindilaurate catalyst in place of said bismuth-containing carboxylatecatalyst, wherein the amount of said dibutyltin dilaurate catalyst insaid comparative coating layer is at least four times higher than theamount of said bismuth-containing carboxylate catalyst in said coatinglayer.
 17. The liner of claim 16, wherein said bismuth-containingcarboxylate catalyst is present in said reaction system in an amount inthe range of from 2 to 14 weight percent, based on the total weight ofsaid silicone diol.
 18. The liner of claim 16, wherein saidbismuth-containing carboxylate catalyst comprises bismuth or acombination of bismuth and zinc.
 19. The liner of claim 16, wherein saidreaction system further comprises at least one solvent selected from thegroup consisting of heptane, toluene, and combinations thereof.
 20. Theliner of claim 16, wherein the degree of cure measured by extraction inn-heptane is statistically the same for said release liner and saidcomparative release liner.